Dawn Causey always assumed that she would sail into menopause with hormone replacement therapy. Her mother has taken hormones for decades, and Causey had no reason to believe she would do otherwise.

But yesterday Causey, a trade association lawyer in her forties, was searching the Internet for alternatives after a medical study was abruptly halted by researchers who concluded that a hormone treatment prescribed for millions of women may have done them more harm than good.

"Now we don't know what to do," said Causey, who is approaching the age when she will have to make a decision. She echoed the lament of many women who flooded doctors' offices and pharmacies with phone calls yesterday. Some were angry, but most were just afraid.

The study was the topic of the day in countless conversations among friends and colleagues as women digested the sobering news that a common combination of estrogen and the synthetic progestin caused some statistically small increases in heart attacks, breast cancer, strokes and blood clots. They also feared that giving it up could mean an acceleration of bone loss and a return of hot flashes and night sweats.

"It's scared a lot of people," said Leonard Rosen, an obstetrician and gynecologist with Fairfax Ob-Gyn Associates, which treats 50,000 patients. "What they're all asking is, 'What should I do now?' "

For now, many doctors said they are advising women not to panic and are scheduling appointments to discuss the latest data and make individual assessments.

Most physicians have a panoply of alternatives, including natural hormones, they noted.

The concern was touched off when researchers running the federally funded Women's Health Initiative announced this week that the largest U.S. trial of combination hormone therapy in healthy postmenopausal women had been stopped three years early because of an increase in breast cancer cases among hormone users.

Increases in heart attacks, strokes and blood clots also led the oversight committee to halt the study.

Overall, the researchers concluded that the treatment was hurting the test subjects more than it was helping them.

That assessment applied to women taking estrogen and progestin, but not to women in a separate study evaluating the use of estrogen alone. Women who have had a hysterectomy are often prescribed estrogen only.

Researchers said that they had not detected any significant increase in breast cancer among women taking estrogen only and that the study would continue because the risks and benefits of estrogen treatment remain uncertain.

The scientists also emphasized that for an individual woman taking estrogen and progestin, the added risk of breast cancer, a heart attack, a stroke or a blood clot was small. They said women suffering from severe menopausal symptoms could reasonably decide to take hormones for a short time.

But they recommended that women no longer consider combination hormone therapy to protect themselves from osteoporosis or other chronic diseases.

For some women, the study prompted an immediate change. In Bethesda, the Glen Echo Pharmacy received three calls from women who said they were switching to another hormone on their doctors' advice.

Barry Aron, chief of obstetrics and gynecology at Civista Hospital in La Plata, has advised several patients who fit the profile of the women in the study to stop taking the drug.

"I felt the risk was more than the benefit at this point," said Aron, who plans to sift through his patient files and write letters asking patients to call or come in to discuss their treatment. "If they were concerned enough to stop the study, that's a pretty big statement."

At the University of Virginia, patients calling the Women's Place, a midlife clinic, were advised to start tapering off the combination if they had been taking it for more than five years, said Melissa Dean-McKinney, a registered nurse at the clinic.

"We're weaning them," she said. "We don't advise anyone to stop cold turkey. It's not dangerous. But the discomfort level could be very disconcerting."

So many concerned patients have called that the clinic has scheduled informational meetings through the weekend and plans to hold a larger one in a hotel conference room.

Despite its unsettling conclusions, the study will not spell the end to hormonal therapy.

"Sometimes hot flashes are so debilitating that people cannot do their daily activities," said Chasheryl Leslie, an obstetrician and gynecologist in Bowie. "In that case, after you sit down and explain the risks and benefits, they still might opt for it."

Some women, however, may be more skeptical of their physicians' advice. Several expressed outrage over the study's findings, saying they believe that the medical establishment has not done right by women in the more than three decades that doctors have been prescribing hormones to healthy women.

"How could we have been misled for so long?" asked Judith Mueller, president and executive director of the Women's Center, a Fairfax County nonprofit organization that provides legal, financial, psychological and job training for Washington area women.

"How could it possibly be that people who are dependent on a medical establishment could be so duped? What is it that is lacking between the drug manufacturers and the doctors and the research on women's bodies that for these many years the information was never defined, correlated and incorporated in our health care?" she said.

Judi Hasson, editor at large for Federal Computer Week, has been wearing an estrogen patch for three years. Although the report described the risks and benefits of estrogen alone as uncertain, Hasson isn't in a trusting mood.

"What really hit home was that women over the age of 45 have really been guinea pigs for a long time," she said.

Staff writers Colleen Jenkins, Theola Labbe{acute} and Susan Okie contributed to this report.